package com.shanduo.newretail.util;

/** 
 * Created by xiang.li on 2015/2/26. 
 */  
public class MD5Utils {  
    /** 
     * 单例
     */  
    private static MD5Utils instance;  
  
    /** 
     * 四个链接变量 
     */  
    private final int A = 0x67452301;  
    private final int B = 0xefcdab89;  
    private final int C = 0x98badcfe;  
    private final int D = 0x10325476;  
  
    /** 
     * ABCD的临时变量 
     */  
    private int Atemp;  
    private int Btemp;  
    private int Ctemp;  
    private int Dtemp;  
  
    /** 
     * 常量ti 
     * 公式:floor(abs(sin(i+1))×(2pow32) 
     */  
    private final int[] K = {  
                0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,  
                0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501, 0x698098d8,  
                0x8b44f7af, 0xffff5bb1, 0x895cd7be, 0x6b901122, 0xfd987193,  
                0xa679438e, 0x49b40821, 0xf61e2562, 0xc040b340, 0x265e5a51,  
                0xe9b6c7aa, 0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,  
                0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed, 0xa9e3e905,  
                0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a, 0xfffa3942, 0x8771f681,  
                0x6d9d6122, 0xfde5380c, 0xa4beea44, 0x4bdecfa9, 0xf6bb4b60,  
                0xbebfbc70, 0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,  
                0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665, 0xf4292244,  
                0x432aff97, 0xab9423a7, 0xfc93a039, 0x655b59c3, 0x8f0ccc92,  
                0xffeff47d, 0x85845dd1, 0x6fa87e4f, 0xfe2ce6e0, 0xa3014314,  
                0x4e0811a1, 0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391  
    };  
  
    /** 
     * 向左位移数,计算方法未知 
     */  
    private final int[] s = {  
            7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7,  
            12, 17, 22, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20, 5, 9, 14, 20,  
            4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 6, 10,  
            15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21  
    };  
  
    /** 
     * 私有构造函数 
     */  
    private MD5Utils() {  
  
    }  
  
    /** 
     * 单例模式 
     * @return 
     */  
    public static MD5Utils getInstance() {  
        if (instance == null) {  
            instance = new MD5Utils();  
        }  
        return instance;  
    }  
  
    /** 
     * 初始化函数 
     */  
    private void init() {  
        Atemp = A;  
        Btemp = B;  
        Ctemp = C;  
        Dtemp = D;  
    }  
  
    /** 
     * 移动一定位数 
     * @param a 
     * @param s 
     * @return 
     */  
    private int shift(int a, int s) {  
        return (a << s) | (a >>> (32 - s)); // 右移的时候，高位一定要补零，而不是补充符号位  
    }  
  
    /** 
     * 主循环 
     * @param M 
     */  
    private void mainLoop(int[] M) {  
        int F;  
        int g;  
        int a = Atemp;  
        int b = Btemp;  
        int c = Ctemp;  
        int d = Dtemp;  
  
        for (int i = 0; i < 64; i++) {  
            if (i < 16) {  
                F = (b & c) | ((~b) & d);  
                g = i;  
            }else if (i < 32) {  
                F = (d & b) | ((~d) & c);  
                g = (5 * i + 1) % 16;  
            }else if (i < 48) {  
                F = b ^ c ^ d;  
                g = (3 * i + 5) % 16;  
            } else {  
                F = c ^ (b | (~d));  
                g = (7 * i) % 16;  
            }  
  
            int tmp = d;  
            d = c;  
            c = b;  
            b = b + shift(a + F + K[i] + M[g], s[i]);  
            a = tmp;  
        }  
  
        Atemp += a;  
        Btemp += b;  
        Ctemp += c;  
        Dtemp += d;  
    }  
  
    /** 
     * 填充函数 
     * 处理后应满足bits≡448(mod512),字节就是bytes≡56（mode64) 
     * 填充方式为先加一个0,其它位补零 
     * 最后加上64位的原来长度 
     * @param str 
     * @return 
     */  
    private int[] add(String str) {  
        int num = ((str.length() + 8) / 64) + 1;    // 以512位，64个字节为一组  
        int[] strByte = new int[num * 16];  // 64/4=16，所以有16个整数  
  
        for (int i = 0; i < num * 16; i++) {  
            // 全部初始化为0  
            strByte[i] = 0;  
        }  
  
        int j;  
        for (j = 0; j < str.length(); j++) {  
            strByte[j >> 2] |= str.charAt(j) << ((j % 4) * 8);  // 一个整数存储四个字节，小端序  
        }  
        strByte[j >> 2] |= 0x80 << ((j % 4) * 8);   // 尾部添加1  
  
        // 添加原长度，长度指位的长度，所以要乘8，然后是小端序，所以放在倒数第二个,这里长度只用了32位  
        strByte[num * 16 - 2] = str.length() * 8;  
  
        return strByte;  
    }  
  
    /** 
     * 调用函数 
     * @param source 原始字符串 
     * @return 
     */  
    public String getMD5(String source) {  
        // 初始化  
        init();  
        int[] strByte = add(source);  
        for (int i = 0; i < strByte.length / 16; i += 16) {  
            int[] num = new int[16];  
            for (int j = 0; j < 16; j++) {  
                num[j] = strByte[i * 16 + j];  
            }  
            mainLoop(num);  
        }  
        return changeHex(Atemp) + changeHex(Btemp) + changeHex(Ctemp) + changeHex(Dtemp);  
    }  
  
    /** 
     * 整数变成16进制字符串 
     * @param a 整数 
     * @return 
     */  
    private String changeHex(int a) {  
        String str="";  
        String tmp = "";  
        for(int i=0;i<4;i++) {  
            tmp = Integer.toHexString(((a >> i * 8) % (1 << 8)) & 0xff);  
            if (tmp.length() < 2) {  
                tmp = "0" + tmp;  
            }  
            str += tmp;  
        }  
        return str;  
    }  
}
